This invention relates to liners or inflations for teat cup assemblies of vacuum-operated milking machines and, more particularly, to such liners or inflations including a milking tube section which extends from the teat cup shell and is attached to the nipple of the milking machine claw.
Automatic milking machines employ teat cup assemblies including a hollow, rigid outer shell which is attached to a pulsating vacuum line and a resilient, tubular liner or inflation installed in the shell in a manner to form a seal at both ends of the shell. A cow's teat is inserted into the upper end of the inflation and the lower end is connected to a claw nipple of the milking machine. During the milking operation, the teat cup assembly is suspended from a cow's teat, primarily by engagement between an opening or mouth in the upper or head end of the inflation and the cow's teat, and milk flows through the inflation under the influence of a vacuum maintained in the milking machine claw.
In the past, the inside diameter of the flow passage through the milking tube section could be relatively small because milk flow was quite low. The milking tube section was quite flexible because the small inside diameter permitted the walls to be made relatively thin yet still not collapse when subjected to a vacuum during the milking operation. This flexibility permitted the teat cup assembly to be conveniently lifted up and slipped onto a cow's teat without imparting a significant side force on the teat.
Modern dairy cows produce milk at substantially higher flows and, consequently, it has become necessary to increase the inside diameter of the flow passage through the milking tube section in order to accommodate this increase in milk flow. As the inside diameter of the milking teat is increased, the wall thickness also must be increased to prevent the walls from collapsing during the milking operation. The increased wall thickness makes the milking tube section relatively stiff.
This stiffness resists movement of the teat cup assembly into a proper orientation for attachment to a cow's teat and can cause the mouthpiece of the inflation to engage a cow's teat at an angle and/or to exert a side force on the teat. This can cause discomfort for the cow. More importantly, such a side force can cause the opening to become slightly distorted, resulting in a non-uniform seal around the teat and undesirable admission of air through the mouthpiece which can cause slippage and produce unhealthy conditions for the teat.
The spacing between teats on a cow's udder can vary considerably from one cow to another in the same herd. Bending for narrowly spaced teats can require minimal bending. Installing inflations on cows with wider spaced teats can require bending of the milking tube up to approximately 90.degree. in some cases, particularly when a cow's udder is lower than normal. Thus, the milking tube must be designed to accommodate the bending required, in both the vertical and horizontal directions, for a wide range of teat spacings and udder heights.
A herd of typical size usually has one or more cows with a missing teat or a malformed, diseased or damaged teat which cannot be milked, or a teat which milks faster than the other teats. When one of these conditions exists and the milking system is operating, one or more teat cup assemblies may not be attached to a teat. The flow passage of the milking tube of the unused teat cup assembly should be closed in some manner to shut off communication between the milking machine claw and the inflation to preserve a vacuum in the system. Typically, the outer end of the claw nipple is beveled and the lower end of an inflation is arranged so that, when a teat cup is disengaged from the teat and the inflation becomes suspended from a claw nipple, the inner wall of the inflation sealingly engages the beveled end of the claw nipple or the walls crimp together at a location beyond the claw nipple.
A more assured and controllable way for shutting off vacuum to an unused teat cup assembly would be to fold the teat cup assembly back over the milking tube section far enough to crimp the flow passage shut and lay the teat cup assembly across the top of the milking machine claw. This could be accomplished relatively easily with inflations having thin walled milking tubes. However, conventional inflations for higher milk flow are not arranged to permit the teat cup assembly to be folded over far enough to crimp the flow passage shut and remain in such a position.
U.S. Larson Patent Nos. 4,745,881 ("'881 Patent") and 4,756,275 ("'275 Patent"), both assigned to the assignee of this application, disclose thick-walled inflations designed to permit the teat cup assembly to be bent at an angle relative to the milking tube section for installation on a cow's teat for milking and yet prevent kinking which causes a reduction in the internal cross-sectional area of the milk flow passage. The '275 Patent discloses the use of a circumferentially extending groove adjacent the lower end of the teat cup shell for this purpose. While such an arrangement is quite satisfactory from the standpoint of minimizing kinking of the milking tube when an inflation is installed on a cow's teat, this groove does not permit the teat and assembly to be folded over toward the milking tube and lie across a milking machine claw because the teat cup shell wedges against the milking tube. The '881 Patent discloses the use of a plurality (up to 7) of circumferentially extending grooves arranged to define segments which abut to prevent bending which can cause kinking during installation of an inflation on a cow's teat. Like the inflation disclosed in the '275 Patent, the inflation disclosed in the '881 Patent is satisfactory from the standpoint of resisting kinking when installed on a cow's teat for milking. However, it is so flexible that the teat cup assembly cannot be folded over the milking tube without sufficient kinking to close off the flow passage through the milking tube.